docs: know issue separate browser for each file (#72)

* docs: know issue: separate browser for each file

* Update README.md

README.md

@@ -194,6 +194,10 @@ jest.setTimeout(35 * 1000);
 
 in your tests at the top. (30 seconds is the default Playwright timeout for waiting for an specific element.)
 
+### New Browser instance for each test
+
+If for your individual tests a new entire browser instance spins up each time and it won't be reused, then you probably run them in parallel. If you run them in a synchronous way with the `--runInBand` CLI option for Jest, then the same browser instance will be re-used and this should fix the issue.
+
 ## Inspiration
 
 Thanks to [Smooth Code](https://github.com/smooth-code) for great [jest-puppeteer](https://github.com/smooth-code/jest-puppeteer).